If there's one thing 19-year-olds aren't supposed to be able to do in the NBA, it's make 3-pointers.

At 23 feet, nine inches, the line is three feet farther than what they attempted during their one-and-done college careers, and four feet beyond the high school game.

Extending your range by that much takes physical maturity, not to mention practice. Most teenagers have no say over the former, and the latter requires time.

And then Jayson Tatum came along.

The Celtics rookie isn't just making 3's. He's raining them. In Tuesday's 111-100 victory over the Bucks, Tatum went 4-for-5 from beyond the arc, his only miss a buzzer-beating heave to end the first half. He drilled all four of his attempts in the first quarter and finished with 17 points on only six shots.

The makes continued what has been an historic start for the rookie out of Duke, upping his season percentage to a league-leading .513.

To put this number in perspective, no teenager has ever made 40 percent of their 3's in a season, let alone 50. Tatum's teammate, Celtics guard Kyrie Irving, came the closest, making 39.9 percent as a rookie in 2010-11, missing the 40 percent barrier by one shot.

As it is, there are only eight other members of the 35 percent club, and they include All-Star-caliber players like Bradley Beal and Stephon Marbury, as well as future Hall of Famer Kobe Bryant.

What makes Tatum's marksmanship so surprising, however, is that he wasn't much of a 3-point shooter at Duke. He made 34.2 percent of his attempts during his lone season with the Blue Devils, profiling instead as an intermediate scorer who could make midrange jumpers or put the ball on the floor a la Raptors All-Star DeMar DeRozan.

But when Gordon Hayward was lost for the season with a broken ankle, the Celtics needed someone to fill the void on the wing, and Tatum has stepped up in a major way.

"Guys that can score, the ball finds the net. It just happens, right?" Celtics coach Brad Stevens told reporters on Tuesday. "But when he came in for his workout, he made a lot of shots. It looked effortless, and that's usually a pretty good sign. It didn't look like it was just one of those days where he was hitting everything. He would miss two in a row and it wouldn't dissuade him from hitting the next one. He had no thought about making the next five -- he just kind of kept shooting it. For a guy with his frame, he shoots it effortlessly. I mean, he's going to be able to shoot it deeper, right? And he's going to be able to make it off running, once he gets a little bit stronger, more used to it, and everything else. He's going to be a heck of a shooter."

Tatum exhibited poise on Tuesday by taking what the defense gave him on either wing. The Bucks closed aggressively in the first quarter in an attempt to deny the extra pass into the corner. Tatum swished one shot in rhythm, knocked down two more after side-stepping defenders, and sank his last one with a man in his face.

"They were actually baiting him to shoot the ball and he just wasn't hesitating," said teammate Al Horford. "He was right there with rhythm. They closed out, he took a dribble. He took his time. It was just a lot of fun to see him have some success early and I feel like because of those 3's, he kind of opened the game up for the rest of us."

Whether this can continue at anything approaching its current level remains to be seen, though it's unlikely Tatum will shoot 50 percent all year.

What's already clear is that Danny Ainge knew what he was doing when he traded out of the top spot in the draft for Tatum, earning another first-rounder in the process. Tatum is averaging 13.9 points a game, ninth on the all-time list for a teen. Five of the players ahead of him are headed to the Hall of Fame (Carmelo Anthony, LeBron James, Kevin Durant, Irving, Bryant), and the other three either played in an All-Star Game or almost certainly will some day (Andrew Wiggins, Stephon Marbury, Beal).

That Tatum has already placed himself in that group is mildly surprising. That he's doing it from downtown is downright shocking.